The present invention relates to an ignition apparatus for internal combustion engines, and particularly to an ignition apparatus for multi-cylinder internal combustion engines not using a high voltage distributor.
A contactless ignition apparatus of this type has already been proposed in, for example, Japanese Patent Laid-Open No. 50263/1981. This apparatus has first and second sensors provided to correspond to the number of cylinders (for instance, two cylinders) of an internal combustion engine, and has first and second ignition coils that generate a secondary voltage to produce sparks for the internal combustion engine. The sensors are crank angle sensors that detect the igniting positions relying upon the turning of the rotor rotated by the engine. An igniting position control circuit and a conduction control circuit are operated by the signals from these sensors, the igniting positions and the conduction initiating positions are determined by an arithmetic circuit relying upon the outputs of these circuits, and the individual switching elements are controlled by the outputs of the arithmetic circuit thereby to control an electric current that flows into the ignition coils. Furthermore, provision is made of AND circuits in a number corresponding to the number of ignition coils, as well as n/2 flip-flop circuits when the number of AND circuits n is an even number, or (n+1)/2 flip-flop circuits when the number of AND circuits n is an odd number.
Operation of this apparatus will be explained below with reference to FIG. 1, which is a wave-form diagram.
Detection signals A of the first sensor and detection signals B of the second sensor are combined, and flip-flop circuits are operated to obtain rectangular output signals C. Signals obtained from the igniting position control circuit and the conduction control circuit, with the signals C as a reference, are modified by the arithmetic circuit to obtain signals D that include signals for the first and second cylinders. Then, depending upon the output condition of a distributing flip-flop, the signals are distributed. For example, when the signal E of the distributing flip-flop has a level of "1" (high level), the signal D, having a high level, is distributed as a signal F for the first cylinder through a logic gate. When the signal E has a level of "0" (low level), the signal D, having a low level, is distributed as a signal G for the second cylinder via a logic gate. The thus distributed signals energize the first and second switching elements, whereby a primary current represented by a signal H flows into the first ignition coil, and a primary current represented by a signal I flows into the second ignition coil. Therefore, an ignition spark J generates in the first cylinder at the time of ignition for the first cylinder, and an ignition spark K also generates in the second cylinder. Namely, depending upon the output condition of the distributing flip-flop, i.e., depending upon the signals E, the signals D that have been combined for the first and second cylinders are distributed as signals F and signals G for each of the cylinders. Therefore, when the output conditions of the distributing flip-flop or the signals E do not properly correspond to the crank angle position of the engine, the ignition signal to be distributed to the first cylinder is erroneously distributed to the second cylinder, or conversely, the ignition signal to be distributed to the second cylinder is erroneously distributed to the first cylinder, resulting in erroneous ignition.
FIGS. 2 and 3 are diagrams of wave forms in the cases of cranking operation. The ignition will be described below more concretely with reference to these drawings.
Crest values in the outputs of the first and second sensors of the type of tachometer generator change as shown, for example, by signals A and B, accompanying the change in the speed of revolution of the engine that results from the change in torque of the engine or the like. That is, if the instantaneous speed at a given moment is slow, the crest value produced by the sensor becomes low. During the time of cranking, there is generally no need of advancing the ignition timing, and the conduction control circuit does not need to be operated, either. Therefore, the moment at which the primary current starts to flow into the ignition coil has been set to a first or a third crank angle position L1 or L2 (hereinafter referred to as position L1 or position L2) which the sensor will detect, and the moment at which the primary current is interrupted (i.e., the ignition time) has been set to a second or a fourth crank angle position T1 or T2 (hereinafter referred to as position T1 or position T2) which the sensor will detect. In the case of FIG. 2, crest values produced by the sensors exceed the threshold voltage (the voltage at which the flip-flop is activated, indicated by the upper and lower lines) of the flip-flop, and the apparatus as a whole properly operates.
Referring to FIG. 3, however, the signal level at the position T2 detected by the second sensor does not reach the threshold voltage (lower dashed line of FIG. 3B) of the flip-flop during a time period t. This is because the vicinity of position T2 corresponds to the latter half of the compression stroke of the engine where the engine turns most slowly. Therefore, the instantaneous speed of the engine is slow, and the crest value produced by the sensor is low. Upon receipt of the sensor output at the position T2, the flip-flop should have been inverted as represented by the signals C in FIGS. 1 and 2. However, since the crest value is low as described above, the flip-flop is not inverted. Therefore, the level "1" of signal of FIG. 3C at the position L2 and the level "0" of signal of FIG. 3E at the position L2, remain unchanged. The sensor output at the subsequent position L1 is greater than the threshold voltage of the flip-flop, and hence, a set input is sent to the flip-flop which produces the signal C. However, since the flip-flop which produces the signal C has already been set (i.e., C="1"), the set input is processed as an invalid signal, and the signal C maintains a level of "1". This state continues until the flip-flop, which produces the signal C responsive to the sensor output at the subsequent position T1, is reset so that the signal C assumes a level of "0".
Furthermore, the flip-flop which produces the signal E responsive to the sensor output at the position T1 receives a reset input. However, for the same reasons as described above, the signal E maintains a level of "0" until the flip-flop which produces the signal E at the next position T2 is set and inverted to a level of "1".
FIG. 3D has the same wave forms as FIG. 3C. This is because there is no need of controlling the conduction ratio or the ignition timing during the period of cranking, and the wave forms of FIG. 3D become analogous to the wave forms of FIG. 3C.
The signal F assumes the level "1" when the signal D has the level "1" and the signal E has the level "1". The signal G assumes the level "1" when the signal D assumes the level "1" and the signal E assumes the level "0". Namely, if expressed by Boolean equations, F=D.multidot.E, and G=D.multidot.E. Therefore, the signal wave forms become as shown in FIGS. 3F and 3G after the signal D has been distributed by the distributing flip-flop which produces the signal E. Interruption of the primary current from flowing into the first and second coils occurs each time that the signals F and G, respectively, go from a high to a low level. Therefore, the wave form of the primary current of the ignition coil for the first cylinder is as shown in FIG. 3H, and the ignition spark in the first cylinder is as shown in FIG. 3J.
However, the wave form of the primary current of the ignition coil for the second cylinder is as shown in FIG. 3I, and the ignition spark in the second cylinder is as shown in FIG. 3K. It will be understood that although the position T1 corresponds to the ignition time for the first cylinder, the ignition spark is erroneously generated in the second cylinder as indicated by the circular dashed line.
In the conventional ignition apparatus, when the sensor output at the position T2 in time period t fails to reach the threshold voltage of the flip-flop, the ignition spark that should be generated in the first cylinder at the position T1 is generated in the second cylinder, and erroneous ignition resulting from erroneous distribution adversely affects the engine. Concretely speaking, great deviation in the ignition timing gives rise to the occurrence of serious accidents such as damage to the engine.
U.S. Pat. No. 3,757,755 (issued to W. J. Carner on Sept. 11, 1973) discloses an engine control apparatus according to which the ignition timing of each cylinder is calculated by a variable delay circuit using ignition timing signals for a plurality of cylinders, and the calculated results are distributed at a low voltage by a firing logic circuit for each of the cylinders.